Class II Major Histocompatibility Complex (MHC) gene products control the acquisition of mature T cell repertoire, serve as restriction elements for CD+ T cells, ,and are receptors for differentiation signals. These multiple functions of class II MHC antigens place them in a crucial role during immune regulation. Hence our abilities to modulate the immune system ultimately will rely on the ability to modulate class II MHC gene expression. This is of pertinence to a large number of diseases with an immune component such as autoimmune, inflammatory and neoplastic diseases. The focus of this proposal is class II MHC gene regulation in lymphoid cell lines and primary blood lymphocytes. In the past few years, we and others have delineated an array of cis-acting elements important for class II gene expression and identified proteins that bind to these elements. The aims of this proposal are to address several issues that are germaine to our further understanding of class II MHC gene regulation. Accordingly, our aims are as follows: (1) To analyze the functions of proteins with specificity for two conserved elements (X and Y) found in all class II MHC promoters. This will be achieved by in vitro transcription, co-transfection or trans-dominant .suppressive mutations. (2) To determine if proteins binding to the X and Y elements interact. This is based on previous studies from our group showing that the stereospecific alignment of X and Y on the DNA helix is important for their function, implicating interactions among proteins that bind to these elements. This will be achieved by electron microscopic examination, immunochemical procedures, affinity chromatography and chemical crosslinking. (3) To determine the regulation of DRA gene in human blood T lymphocytes activated by different ligands to express class II antigens. Preliminary studies in the laboratory suggest that different activation pathways (such as engagement of the T cell receptor vs. mitogen stimulation) require different sets of regulatory elements. Similar studies will be further extended to DR- expressing T lymphocytes from inflammatory autoimmune rheumatoid arthritis to determine if their promoter element usage is similar to that of known ligands. These goals will further our comprehension of class II gene regulation at the molecular and biologic levels.